Enzyme-Linked Immunosorbent Assay (ELISA) is a commonly used test used for medical diagnostics and to test for the presence of molecular contaminants such as pesticides and water and food contaminants. The ELISA test is very sensitive (˜picogram per ml) but takes hours to run by a highly skilled technician. In addition the ELISA test requires several sequential chemical reactions that are time sensitive and handling sensitive. Expensive optical equipment is required to read the results.
Electronic sensors such as, for example, biochemical and ion sensitive field effect transistors (bio-FETs and ISFETs) overcome the key limitations of optical sensors. They are a low cost, one step test that gives results in a manner of minutes and do not require a highly trained technician to run the test or expensive optical equipment to read the test.
FETs are natural candidates for electrically-based sensing of charged analytes due to the dependence of channel conductance on both gate voltage and surface charges resulting from the binding of biomolecules to the channel surface. ISFETs have been developed for over 30 years and are reliable electronic biochemical sensors for real-time measuring pH values of liquid and in-line quality monitoring of milk, beer, yogurt, and the like.
Recently, fin-FETs with nanowidth channels have been developed which provide detection limit down to parts per billion (ppb) for gas detection and femtomolar (fM) or femtogram/ml for detection in solution which is comparable with most advanced optical sensors. The high sensitivity is attributed to nano width (100 nm or less) of the fin-FET channels which are comparable to the device Debye length and size of biomolecules. In nanowidth fin-FETs, the entire channel may be fully modulated by the charge on biomolecules binding to the gate dielectric significantly increasing sensitivity.
As described above, the nanowidth finfET shows great potential in becoming a truly low cost, ultra-portable, and highly sensitive sensor platform for meeting future biosensing applications. However, there are still important challenges for this type of sensor to be practically useful. The challenges may be, for example, poor stability, poor reproducibility, and poor reliability when using physiological samples such as, for example, whole blood, serum, saliva, and the like. The poor reliability of device itself and their bio-abio surfaces means that at present finFET biosensors cannot be made reproducibly and uniformly.